The general aim of the proposed research is to determine the properties of the early photochemical changes in cone visual pigments during photolysis. The long range goal of this research is to arrive at a clearer understanding of the role of the intermediate products of bleaching in the transduction of light into a neural signal by photoreceptor cells. The early receptor potential (ERP) is closely related to the early events in the photolysis of the cone pigments. As such, the potential change associated with the ERP provides a means of studying the properties of these events. ERP's recorded with internal electrodes from cones in the turtle retina will be analyzed to determine the spectral characteristics, temperature dependence and kinetics of the intermediate transitions in pigment molecules underlying generation of these voltage changes. In addition, an attempt will be made to record voltage changes generated by photoregeneration of the cone pigment from its intermediate products. If successful, this will provide a means of determining the spectral sensitivity of the intermediate products. Finally, the ERP will be used to follow changes in pigment concentration in the cell during bleaching and regeneration and to relate the changes to changes in receptor sensitivity.